1. Technical Field
The invention relates to a process for preparing fiber reactive dyes.
2. Background
The preparation of fiber reactive dyes based on 6-amino-4-hydroxy-2-naphthalenesulfonic acid and 7-amino-4-hydroxy 2-naphthalenesulfonic acid derivatives is known. These fiber reactive dyes may be represented by the following general formula: ##STR1## in the above formula, the amino linking group may be in the 6, or 7 ring position on the naphthalene ring. The moiety D represents a phenylene or an naphthylene group. R.sub.1 and R.sub.2 are independently selected from hydrogen, sulfo, phosphato, carboxy, hydroxy, C.sub.1 to C.sub.4 alkyl, C.sub.1 to C.sub.4 alkoxy, aryl and halo; R.sub.3 and R.sub.4 are independently selected from hydrogen and C.sub.1 to C.sub.4 alkyl with n and n' are independently equal to an integer of 1 to 3. The moiety X is selected from chloro, fluoro or --NHCN. The moiety SO.sub.2 Y is a fiber reactive group wherein Y represents a vinyl group (--CH.dbd.CH.sub.2) or the moiety --CH.sub.2 CH.sub.2 Z wherein Z represents a leaving group capable of being split off in an alkaline medium.
The prior art processes for preparing compounds of the above general formula are described in Japanese Patent Publication 59-4653. In one of the prior art processes, the diazo coupling is done at 0.degree.-30.degree. C. In the second process, the amino group on the naphthalenesulfonic acid coupler is acylated with acetic anhydride or acetyl chloride prior to coupling the naphthalenesulfonic acid with the diazonium salt. After the coupling reaction is completed it is necessary to deacylate the reaction product by base-catalyzed high temperature hydrolysis. The deacylated product is then condensed with a fiber reactive anchor moiety e.g. a fiber reactive anchor prepared from the condensation product of aniline-4-(2-sulfatoethyl) sulfone and cyanuric chloride. The reaction sequence is illustrated in FIG. 1.
The acylation-deacylation process of japanese Patent Publication 59-4653 was practiced in the prior art in order to minimize the formation of undesired isomers which are pH sensitive (see e.g. Zollinger, H., Color of Chemistry, Weinheim; New York: VCH, 1987). The isomer depicted in Formula 1 is believed to be the desired product and it is not pH sensitve. In this desired isomer, the diazonium coupling takes place ortho to the hydroxyl group in naphthalenesulfonic acid coupler. However, the prior art coupling reaction of the naphthalene sulfonic coupler (nonacylated) produces appreciable quantities another isomer wherein the diazonium coupling takes place para to isomer, a shift from a yellow shade to a red and dull shade under increasing pH is observed.
The process of the present invention eliminates the need to acylate and deacylate and therefore eliminates undesired formation of acetic acid or sodium acetate by product waste streams which must be treated before discharge to the environment. The process of the invention also provides a method ##STR2##
whereby the formation of the undersired para isomer is substantially reduced with an attendant increase in product yield, product quality and process productivity.